(Reuters Health) - Electromagnetic fields produced by motors in electric cars don’t appear strong enough to interfere with implanted heart devices like pacemakers and defibrillators, a small German study suggests.

Inverter and motor unit are seen inside the Nissan Leaf in Tokyo, Japan October 25, 2017. REUTERS/Kim Kyung-Hoon

All electric motors can produce electromagnetic fields. If these fields are strong enough, they have the potential to disrupt the normal function of implanted heart devices, researchers note in the Annals of Internal Medicine. Pacemaker malfunctions might cause the heart to stop beating with potentially fatal results, while defibrillators might respond to electromagnetic fields by delivering unnecessary shocks to patients’ hearts, causing pain and anxiety.

For the study, researchers measured the magnetic field strength in four electric cars with the largest market share in Europe: the BMW i3, Nissan Leaf, Tesla Model 85S, and the Volkswagen e-up!

They also assessed how well pacemakers and defibrillators worked for 108 patients with these implanted cardiac devices who sat in the cars during simulated driving and charging tests.

None of the cars appeared to interfere with patients’ heart devices, the study found.

“Our study suggests that the electromagnetic fields generated by electric cars do not cause malfunctions,” said lead study author Dr. Carsten Lennerz of the German Heart Center Munich and the German Center for Cardiovascular Research.

While the results are promising, the designs of electric cars as well as pacemakers and defibrillators are constantly changing and it’s possible what happened for the specific cars and heart devices in the study might not reflect what every patient would experience, Lennerz cautioned.

“Patients with pacemakers and defibrillators should see these results as encouraging for their safety in electric cars, but should be wary that rare events may still occur,” Lennerz said by email.

It’s possible that devices didn’t malfunction in the study because the car batteries, electric motors and other components have electromagnetic shielding, Lennerz said by email. It’s also possible that the pacemakers and defibrillators have technology to help prevent the devices from responding to any signals from the cars.

For the study, researchers asked patients with pacemakers and defibrillators to sit in one of four different electric cars and to charge the car’s battery using charging cables. Researchers measured the magnetic field inside and next to the cars as they were operated and next to the charging cables during charging.

Researchers also monitored patients’ pacemakers and defibrillators for any indication of interference during the experiment.

The study, however, might not have been large enough to detect rare problems or accurately reflect what might happen across a broad population of people with heart problems who rely on pacemakers and defibrillators, the authors note.

“It seems to be reassuring but when we consider that millions of electric cars will be sold it is reasonable to think that larger numbers of cardiac implanted electric device patients should be studied,” said Dr. Richard Sutton of Imperial College, London, in the UK.

“If patients could not be near or travel in an electric car this could be disastrous for patients but more so for the direction of the auto-industry and for the potential benefits of reversing global warming,” Sutton, who wasn’t involved in the study, said by email. Sutton has received grant, consulting and speaking fees from several major medical device companies.

Another drawback is that the battery power of electric cars might increase in the future, making them more dangerous to these heart patients, said Dr. Dhanunjaya Lakkireddy of the University of Kansas Hospital in Kansas City.

“Over the last few decades we have learnt that very simple household items like electric razors, blow dryers, microwaves, induction ovens, etc., have shown to interfere with cardiac implanted electrical device function,” Lakkireddy, who wasn’t involved in the study, said by email.

“Patients should feel confident that the current generation electric cars should not have any significant impact on their device function,” Lakkireddy added. ‘However what is to happen when the battery power that is packed inside these cars significantly increases with time is yet to be well understood.”